ptrace replaces procfs? Wow, that's a disappointing turn of events. It's also against the flow of thought in the Unix community I knew in 1980. If somebody has any of the old ca-1980 BSD manuals, you should find a BUGS section on ptrace advocating a move to a file-system-like interface. I always assumed ken wrote that little note when he was visiting UCB -- anybody know?
Plan 9 implements process debug via /proc, and several debuggers use that interface
....The file system model is powerful. The strace based on /proc was a few dozen lines.